The Environmental Fluids Group of the Department of Geography and Environmental Engineering, lead by Dr. Marc Parlange, is currently involved in two air pollution projects that benefit from the capabilities of the JHU scanning elastic backscatter lidar system.
Much of what is known about the structure of the atmospheric boundary layer (ABL) has been observed with elastic backscatter lidar (light detection and ranging) systems, a laser beam that scatters off of aerosols, giving a two dimensional image of particles in the ABL. Such information is needed to support development of State Implementation Plans and the setting of National Ambient Air Quality Standards; hence lidars are well suited for air pollution studies as well as investigations that try to improve the general understanding about boundary layer processes.
The Baltimore Particulate Matter (PM) Supersite project aims at providing highly time and size resolved concentrations of urban PM2.5 (airborne Particulate Matter with aerodynamic diameter less than 2.5 microns) and its constituents, including an indicator of cardiopulmonary response in support of testing hypotheses relating to source attribution and health effects of PM.
Apart from the JHU lidar, the Parlange group operates a micrometeorological station as well as a spectroradiometer. This, together with a large number of instruments to determine aerosol size and composition, allows the science team to study ambient air quality in Baltimore in great detail. The lidar plays in important role, as it provides valuable information such as the boundary layer height, which defines the volume in which aerosols can mix. Turbulent air in the growing ABL typically contains more aerosols than the cleaner entrained atmosphere at the top of the ABL.
As this cleaner air is entrained, it mixes with the lower level air, diluting aerosol concentrations. Unfortunately this dilution process is not well captured by vertically pointing lidar systems. For example, in the beginning of July 2002, particulates from forest fires in Quebec, Canada, drifted over Maryland, providing the Parlange group with a unique opportunity to measure and observe entrainment into the ABL.
The lidar measurements that were taken distinctly revealed the downward sweeps (or wisps) of free atmosphere into the ABL. In this case, the entrained air contained more particulates than the lower level ABL air, highlighting atmospheric motion in an unprecedented fashion.
The first results from the analysis of the data collected so far were presented at this years AAAR (American Association for Aerosol Research) meeting in Charlotte, N.C.
The second project, part of the Hazardous Substances Research Center directed by Dr. Ed Bauer, is concerned with the dispersion of aerosol plumes from smoke stacks in Baltimore. In this project both experimental work and computational modeling (large-eddy simulation) are employed. Lidar scans give an opportunity to study the time evolution of plume height and width as well as the dispersion of the aerosol plume downwind of the stack.
The experimental data will be used in an a posteriori mode by the Parlange group in collaboration with Dr. Charles Meneveau, from the Mechanical Engineering and Geography and Environmental Engineering departments, to assess the performance of their JHU large eddy simulation model, which has been refined such that it allows for simulations of particle transport in an urban environment.
Both projects, still ongoing, are important collaborative efforts to better understand processes that govern air pollution in Baltimore and to assess its implications.
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